Certain resins used for a variety of end use applications, such as polycarbonate, show good impact properties at room temperature but the impact properties deteriorate at lower temperature. Use of impact modifiers helps preserve the impact properties at lower temperatures.
For certain applications such as impact modification of window profiles (particularly in colder climates), there are strong market needs to improve properties such as low temperature impact resistance which does not deteriorate with weathering.
Typically impact modifiers are prepared by emulsion polymerization process and are comprised of up to 95% of a low glass transition temperature (Tg) core, and a high Tg shell, composed primarily of polymethylmethacrylate (PMMA). The PMMA shell prevents the low Tg core from agglomeration when it is isolated from the latex phase. Additionally, the PMMA shell aids in compatibilizing the core with the matrix material. Without the PMMA shell, the effectiveness of the impact modifiers is limited.
For compositions that are prepared with polybutadiene core, the weatherability is typically poor, as the residual unsaturation crosslinks and gets embrittled.
The particle size at which impact modification is most effective is in the range of 50 to 500 nm. Particles of this size are typically made by emulsion polymerization.
Thus far, the chemistries that were available to prepare impact modifiers were limited to the monomers that could be emulsion polymerized. It has not previously been possible to use other chemistries such as olefinic, (which can be effective in impact modification because of good weatherability and low Tg) as no route existed to make small particles with a multi layer structure (for example, core/shell structure).
Currently, functionalized polyolefin pellets have been used directly to compound into another matrix resin, by tuning process parameters, a discrete polyolefin phase can be achieved. However, it is quite challenging to get desired compatibility (limited resin functionality) and particle size and for each specific resin, the process conditions have to be optimized. Additionally it has not been possible to add a shell layer (such as PMMA) to help in compatibilization and stress transfer. To date, there is no olefin powder similar to the acrylic impact modifier with a core-shell structure, where the shell offers good compatibility and the rubber core imparts the impact strength. Typically, aggregated discrete particles (100-500 nm) can be facilely dispersed in a matrix resin. We hypothesize that if the acrylic core is replaced by an olefin elastomer, with the same acrylic shell, such products can be a drop-in replacement for the incumbent acrylic or butadiene based impact modifiers in many systems and in addition it is expected that they bring good performance attributes from polyolefin (e.g. weatherability, and low temperature toughening). To date, there has been no technology available to make such products.